Studies on the structure of macromolecules in cancer cells are essential for defining the biochemical lesion(s) distinguishing cancer cells from normal cells. Since there is ample evidence, mainly from chromatographic studies, for alterations of tRNAPhe in cancer cells but almost no information is available on sequences of human tRNAs we propose to determine the primary structure of tRNAPhe from normal and neoplastic human tissues by novel sensitive tritium derivative methods for sequencing of RNA developed in our laboratory. We plan to concentrate initially on the structural characterization of tRNAPhe from human placenta and liver and at a later stage to sequence tRNAPhe species from human tumors. The tritium derivative methods for sequencing of RNA have been designed in such a way that no in vivo labeling is required and only small amounts of tissue are needed. They are thus particularly suited for structural investigation on human RNAs. The sequencing scheme is based on complete and partial enzymic degradation of the RNA to oligonucleotides, thin-layer chromatographic separation of the digests on PEI-cellulose, isolation of oligonucleotides from the chromatograms, degradation of the oligonucleotides in the presence of NaIO4 and phosphomonoesterase, tritium labeling of the degradation products, and analysis of tritium-labeled components. BIBLIOGRAPHIC REFERENCES: Randerath, K., Chia, L.S.Y., Gupta, R.C., Randerath, E., Hawkins, E.R., Brum, C.K., and Chang, S.H., Structural analysis of non-radioactive RNA by postlabeling: The primary sequence of baker's yeast tRNA Leu CUA, Biochem. Biophys. Res. Comm. 63, 157-163 (1975). Roe, B.A., Anandaraj, M.P.J.S., Chia, L.S.Y., Randerath, E., Gupta, R.C., and Randerath, K., Sequence studies on tRNAPhe from human placenta: Comparison with known sequences of tRNAPhe from other normal mammalian tissues, Biochem. Biophys. Res. Comm. 66, 1097-1105 (1975).